Control and protection of electric circuits



Jam 7 H R SEARENG 2 5327 2634 CONTROL AND PROTECTION OF ELECTRICCIRCUITS Original Filed June 23, 1934 His Attorne g- Patented Jan. 7,1936 2,027,204

UNITED STATES PATENT OFFICE CONTROL AND PROTECTION OF ELECTRIC CIRCUITS7 Hudson R. Searing, New York, N. Y., assignor to General ElectricCompany, a corporation of New York Application June 23, 1934, Serial No.732,049 Renewed November 12, 1935 7 Claims. (Cl. 175-294) My inventionrelates to improvements in the the feeder whether the ground isaccidental as control and protection of electric circuits and a fault orpurposely applied in order to disconmore particularly to improvements inthe connect the feeder from the network. trol and protection ofalternating current net- Another object of my invention is to providework distribution systems and an object of my h a improved arrangementas will not be 5 invention is to provide a control and protectiveaffected by and will not interfere with the high arrangement which isingeneral an improvement voltage direct current tests which are appliedon arrangements heretofore known to the art. to network systems of thetype in question.

In network distribution systems, one or more These and other objects ofmy invention will 10 feeders are connected to the network through pp inmore detail hereinafterl0 step-down transformers and network protectors.My invention will be better understood from Energy directionalresponsive devices are usuthe following description when considered inally associated with the protectors so as to disconnection with theaccompanying draw and connect the network from the feeder when for itsscope will be pointed out in the appended any reason, such as a fault onthe feeder, power claims. 15 flow is from the network to the feeder. Inorder In the single figure of the accompanying drawto isolate feedersfor inspection and maintening, I have shown for the purpose ofillustrating ance and incidentally to save losses, these energy myinvention an embodiment thereof as applied directional responsivedevices have been given to the control and protection of an electricsysa sensitivity of response such as to disconnect the tem comprisingtwo electric circuits 5 and A network from the feeder merely on thereverse illustrated, these are three-phase circuits which flow of powerdue to the magnetizing current of are inductively coupled by atransformer I havthe transformer in a feeder out of service, that logwindings 8 delta-connected to the circuit 5 is, disconnected at thepower station. This deand windings 9 Y-connected to the circuit 6 greeof sensitivity frequently results in unneceswith the neutral point It)grounded. The cir- 3 sary interruptions due to feed back from recuit 5may represent one of a plurality of feeder generating elevator motors orto circulating curcircuits which are arranged to supply the netrentsarising from slight differences in feeder work indicated schematicallyby the conductors voltages. II. The network is connected to therespective In order to avoid such undesired operations, feeders throughsuitable circuit interrupting the energy directional means wasdesensitized or means such as a latched closed circuit breakerrestrained in some manner usually in dependl2. The feeders 5 extend fromone or more powence on the network voltage. But this sacrificed erstations I, which are usually provided with a the desired feederisolation control and also the grounded neutral 2. Each feeder isprovided tripping'on reverse magnetizing current. with fault responsiveprotective means, such, for

While these features are desirable, potential example, as overcurrentrelays 3, only one being deivces for obtaining them must not increasethe shown for simplicity, and suitable circuit interhazard of the systemor reduce its economies of rupting means 4 for opening the feeder at theoperation. Also where it is customary to apply power station on theoccurrence of abnormal cona high voltage D. C. test to the feeders andconditions on the feeder. At the power station the 40 nected equipment,any means provided to give feeder may be provided with means such asathe desired control and sensitivity should be switch 30 for groundingone or more of the feeder able to withstand such high voltage testswithconductors after the station feeder circuit breaker out damage orchange in characteristic and also has opened, as disclosed for examplein British 15 in the event of systems with a large number of Patent396,853. Likewise as disclosed in United 49 transformers connected toone feeder not over- States Letters Patent 1,883,839, issued Octoberload the testing means employed. Further it is 18, 1932, there may beprovided energy directional desirable to be able automatically todisconnect responsive means such as a polyphase power dithe network fromthe feeder by a simple operarectional relay l3 which is responsive tothe ex- 50 tion performed at the station. change of energy between thenetwork and the An object of my invention is to provide an imfeeder toeffect the opening of the circuit breaker proved control and protectivearrangement for l2 when energy flow is from the network to the providingnon-sensitive protection under normal feeder. This relay comprisesvoltage windings l4 operating conditions and yet obtaining a more whichare connected to be energized from the sensitive operation whenever aground occurs on network side of the circuit breaker l2 and cooperatingcurrent windings l5 which are connected to be energized from currenttransformers It on the feeder side of the circuit breaker [2. Also, asdisclosed in the said United States Letters Patent, the relay [3 may beprovided with a restraining or desensitizing means I! which is simplyillustrated as two voltage windings [1. These are connected to beenergized by the potential transformer I9 and to exert a restrainingtorque tending to prevent movement of the relay to the trippingposition.

In accordance with my invention, I provide means responsive to anunbalance of the impedances to ground of the phase conductors of thecircuit 5 which may occur, for example, in case of a ground on thecircuit 5, whether the ground is accidental, as a ground fault, or ispurposely applied through the switch 30 at the power station afterdisconnection of the circuit therefrom, for increasing the sensitivityof response of the relay l3 whereby to insure the disconnection of thenetwork I from the feeder 5 by the opening of the circuit breaker l2. Asshown, this means comprises a circuit or path 20 between the conductorsof the feeder 5 and ground so connected as to be energized in accordancewith the zero phase sequence voltage of the feeder on the occurrence ofa ground on the feeder. Thus circuit 20 maybe coupled to the feeder 5 byresistance or reactance coupling. I have chosen to illustrate the latterschematically by condensers 2| which may be formed in case of cableconductors by an intermediate shield on the cable insulation, althoughinductive reactance coupling may be used as desired. The circuit 20includes means such as an auxiliary relay 24 for controlling therestraint of the restraining means I! when the circuit is energizedsufliciently to cause operation of the relay 24 whereby to sensitize thedirectional responsive relay l3.

' Whenever a phase conductor of the circuit 5 is grounded the circuit 20is energized because the capacitances to ground of the phase conductorsof the circuit 5 are no longer balanced. Sufficient current is therebyenabled to flow in the circuit of the auxiliary relay 24 to cause it toopen its contacts in the circuits of the voltage windings N3 of therestraining means II, whereby to remove the restraint. The amount ofthis current is of course increased when the circuit breaker 4 opensbecause the voltages to ground of the ungrounded conductors go from Yvoltage to delta voltage.

Assuming, for example, a ground fault on the circuit 5, the protectivemeans 3 and 4 at the power station I operate to disconnect the feeder atthe station. The voltage to ground on the ungrounded conductors of thefeeder 5 rises from Y voltage to delta voltage because the feeder isstill energized from the network. The circuit of the auxiliary relay 2%is energized as previously pointed out, and this relay operates toremove the restraint from the relay l3. By reason of the increasedsensitivity the directional relay I3 operates to effect the tripping ofthe circuit breaker H2, in response to the flow of transformermagnetizing current from the network to the feeder.

If it is desired to isolate a feeder from the network at any time, thecircuit of the feeder may be opened at the power station and then one ofthe feeder conductors grounded bythe switch 33. As soon as this is done,the circuit 20 is energized and thevoltage to ground of theungroundedconductors rises from Y voltage to delta voltage. Theauxiliary relay 2% is accordingly energized and operates to sensitizethe direction of relay It as to insure the tripping of the circuitbreaker 12 on the flow of transformer magnetizing current from thenetwork to the feeder.

While I have shown and described my invention in considerable detail, Ido not desire to be limited to the exact arrangements shown but seek tocover by the appended claims all those modifications'which fall withinthe true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In combination, a three-phase feeder circuit, a three-phase networkcircuit, a transformer having windings-connected to the feeder circuitand windings connected to the network circuit, means responsive to thedirection of energy exchange between said circuits for interrupting thenetwork circuit and means connected to be energized in accordance withthe balance of the impedances to ground of the phase conductors of thefeeder circuit for controlling the sensitivity of said directionalresponsive means.

2. In combination, a feeder circuit, a network circuit, a transformerhaving windings connected to said circuits, circuit interrupting meansin said network circuit, means normally responsive only to apredetermined relatively large value of electric energy flow from thenetwork circuit to the feeder circuit for effecting the opening of saidcircuit interrupting means and means connected to said feeder circuitoperative in response to a ground thereon for causing said energyresponsive means to effect the opening of said circuit interruptingmeans in response to a relatively small value of electric energy flowfrom said network circuit to said feeder circuit.

3. In combination, a feeder circuit, a network circuit, a transformerhaving windings connected to said circuits, circuit interrupting meansin said network circuit, means normally responsive only to apredetermined relatively large value of electric energy flow from thenetwork circuit to the feeder circuit for effecting the opening of saidcircuit interrupting means and means responsive to an unbalance of theimpedances to ground of the phase conductors of the feeder circuit forcausing said energy responsive means to effect the opening of saidcircuit interrupting means in response to a relatively small value ofelectric energy flow from said network to said transformer.

4. In combination, two three-phase circuits, a transformer havingwindings connected to said circuits, means responsive to the directionof energy exchange between said circuits for disconnecting one of saidcircuits, control means connected to ground and capacitatively coupledto the other of said circuits for controlling the sensitivity of saidenergy directional responsive means in accordance with the balance ofthe capacitances to ground of the phase conductors of said othercircuit.

5. In combination, two three-phase circuits, a transformer havingwindings delta connected to one of said circuits and windingsY-connected to the other of said circuits, means responsive to thedirection of energy exchange between said circuits for disconnectingsaid other circuit from 7 of said feeder circuit for varying thesensitivity of said fault responsive means.

7. In combination, a polyphase feeder circuit, a polyphase networkcircuit, a transformer having windings connected to said circuits, faultresponsive means for effecting the disconnection of the transformer fromthe network circuit and means operative solely in dependence on the zerophase sequence voltage of the feeder circuit for controlling thesensitivity of said fault responsive 1 means.

HUDSON R. SEARING.

